Various types of energy absorbing bumpers are known in the art. One such type is commonly known as a pneumatic or semi-pneumatic bumper wherein it is intended that air trapped within the bumper will absorb some of the energy of the impact. However, if the bumper is constructed to provide a totally enclosed chamber, the entrapped air actually acts as an energy storing medium as opposed to an energy dissipating medium, and as such, there is a tendency for the bumper to act as a spring imparting a potentially harmful rebound effect following impact.
In another type of pneumatic bumper system the air within the bumper is vented to a storage tank upon impact and then allowed to bleed back to the bumper. While representing an improvement over the totally closed system, such a bumper is limited in its capacity to absorb energy because as air is transferred to the tank and the pressure increase therein, the bumper itself resists further compression.
Non-pneumatic energy absorbing bumpers generally consist of an elastomeric shell which is affixed to the vehicle and includes a plurality of vertical reinforcing ribs therein which are designed to absorb the energy of an impact. As will hereinafter be discussed in greater detail, while effective for certain applications, the energy absorbing characteristics of such bumpers are quite limited and only if they are made unwieldily large could they be suitable for higher vehicle speed impacts.